High Mountain Asia, often called the “Third Pole,” holds the largest store of ice outside the Arctic and Antarctic. Its glaciers have shaped landscapes, nourished rivers, and sustained communities for thousands of years. But today, these frozen giants are shrinking at a troubling pace.

Scientists have long agreed that warming temperatures drive the retreat, yet new evidence reveals another culprit: shifting rainfall and snowfall patterns, especially those tied to the South Asian monsoon.

Glaciers losing ice faster

The numbers are staggering. Glaciers across the region are losing more than 22 gigatons of ice each year, equivalent to nearly nine million Olympic swimming pools.

While rising temperatures explain much of the retreat, researchers from the University of Utah and Virginia Tech show that the timing and type of precipitation now play a major role. Rain falling instead of snow fuels melt, and shorter or weaker monsoon seasons reduce the ice that glaciers can accumulate.

“These findings highlight that glaciers dominated by the South Asian monsoons, such as the Central Himalaya, Western Himalaya and Eastern Himalaya, are especially vulnerable,” said Sonam Sherpa, assistant professor at the University of Utah and lead author of the study.

“If the timing and intensity of the monsoon continues to alter, it could accelerate ice loss and threaten water availability for millions downstream.”

Billions rely on glacier water

The glaciers of High Mountain Asia supply freshwater to more than 1.4 billion people. These rivers sustain agriculture, hydropower, and drinking water across South and Central Asia.

As glaciers retreat more rapidly, rivers will depend less on glacial melt and increasingly on rainfall as their main source of water.

“Looking ahead, a faster retreat of mountain glaciers will shift the main source of river flow from glacier melt to rainfall, thereby heightening the risk of droughts in downstream regions for future generations,” said Susanna Werth, assistant professor at Virginia Tech and co-author of the study.

Monsoon impacts on glaciers

To understand these shifts, the researchers used satellite gravimetry from NASA’s GRACE and GRACE-FO missions. These satellites can “weigh” changes in water storage, including ice, by measuring gravity variations.

Scientists corrected the data to account for groundwater use, soil moisture, surface water, and snow. They paired this with climate reanalysis models, dividing the year into four phases: winter, premonsoon, monsoon, and postmonsoon.

By analyzing rainfall and snowfall separately, they revealed how timing and precipitation type affect glacier mass.

Monsoon timing speeds ice loss

The experts found that glaciers respond more strongly to seasonal precipitation than to annual totals.

Cycles repeating every 3 to 4.5 years and 5 to 8 years match the natural rhythm of South Asian monsoons. In the Central Himalaya, glacier loss was tied to reduced premonsoon rainfall.

In the Eastern Himalaya, declining postmonsoon snowfall accelerated retreat. In the Western Himalaya, increased summer rain caused rain-on-ice events that sped melting. These details show that the seasonality of rain and snow is as important as overall precipitation amounts.

Glacier loss differs by region

Different climate systems influence each subregion. Monsoon-fed glaciers in the Central and Eastern Himalaya show the highest rates of ice loss.

Glaciers dominated by the Westerlies, such as those in the Pamir–Hindu Kush and Karakoram, show slower declines or in some cases slight gains.

The Tien Shan, influenced by Siberian systems and western cyclones, also shows significant losses. These contrasts highlight how winds and precipitation phase shifts shape glacier health differently across the mountains.

Hazards on the rise

Rapid melting brings hazards that are both immediate and long-term. Glacial lake outburst floods are becoming more common as ice retreats, creating unstable lakes held back by fragile moraine walls. Landslides and river floods often follow, putting downstream communities at risk.

“This risk is not only about long-term water shortages but also about immediate threats to lives and infrastructure,” said Sherpa.

Glacier loss under stronger monsoons

Climate projections suggest stronger and more intense monsoons in the coming decades, with possible changes in their timing.

By 2100, ice loss in monsoon-dominated basins could reach 38–58 percent, depending on future emissions.

Such a shift would profoundly affect river flows, agriculture, and disaster risks. The study emphasizes that improved monitoring networks are urgently needed to capture rain, snow, and temperature changes across high-altitude regions.

Protecting communities downstream

High Mountain Asia’s glaciers are retreating under the combined weight of heat and shifting monsoons. Seasonal timing and the balance of rain versus snow now shape their fate more than annual totals.

Protecting communities downstream will require better observation and planning that accounts for these seasonal fingerprints.

The research makes clear that what happens in these mountains will ripple far beyond their valleys, potentially impacting the lives of more than a billion people.

The study is published in the IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing.

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